the damn rear tires?

I jacked the rear end up, removed the lug nut cover, removed the 4 lug nuts, removed the center metal hub cover, and then attempted to remove the rear tire. I couldn't get the thing to budge! Anyone else have this problem? I had my tires rotated about 7,000 miles ago and clearly the tire shop removed the tires so why was it so difficult for me to remove them? Is there something I'm missing? Thanks for the help!